The invention relates to a physiological-signal-analysis device for measuring a blood pressure, and particularly to a device that applies a pressure to a patient and determines whether a detected pressure oscillation satisfies one or more criteria.
There are many known devices for measuring a patient""""s blood pressure. One type of device uses a technique referred to as an oscillometric technique. For this technique, typically, a blood pressure cuff is connected to an arm of the patient and is pneumatically controlled to apply a high pressure to the patient. The pressure is then reduced in steps to a low pressure. For each pressure step (also referred herein as pressure level), a pressure transducer connected with the cuff senses a cuff pressure. The sensed cuff pressure includes the applied pressure and pressure oscillations (also referred to herein as blood pressure oscillations, pressure pulses and blood pressure pulses). The sensed cuff pressure is applied to a control unit that isolates the pressure oscillations and stores two consecutive, matching oscillations at each pressure step. Requiring two consecutive, matching oscillations prevents intermittent artifact from causing the device to seriously err when performing the measurement. Example blood pressure monitors that require two consecutive, matching oscillations are described in RAMSEY M., Blood Pressure Monitoring: Automated Oscillometric Devices, Journal of Clinical Monitoring, 1991, 7 (1), 56-67, which is incorporated herein by reference.
The time duration for measuring a blood pressure depends on the magnitude of the high pressure, the difference in pressure between steps, and the amount of time at each step. With the requirement that the device needs to match consecutive oscillations at each level, the blood pressure determination may be unduly prolonged and the patient may be unduly stressed or inconvenienced. The time for each pressure step is established by the time it takes two consecutive cardiac contractions to produce two, roughly equal pressure oscillations in the cuff. For example, if at a particular pressure step first, third, fifth and sixth pulses match while the second and fourth pulses do not, then the step may be unduly long. This is because the prior art system does not proceed to the next pressure step until after the sixth pulse. Accordingly, it would be beneficial to provide a device for measuring a patient""""s blood pressure where the device includes criteria that allows two nonconsecutive pulses to be matched at a level.
Additionally, for some embodiments, it is beneficial to provide a device for measuring a patient""""s blood pressure where the device relaxes or changes one or more criteria when a known event is occurring. By relaxing one or more criteria, the device allows the measurement to be performed in a timely fashion for some medically unstable patients. Without the relaxed criteria, the measurement may take too long, causing discomfort to the patient and possibly resulting in no blood pressure determination. Relaxing the criteria in a proper fashion will not overly affect the accuracy of the determination.
Accordingly, in one embodiment, the invention provides a method of determining whether an oscillation of a pressure signal acquired from a patient satisfies one or more criteria. The method includes the acts of acquiring a first oscillation having a first fiducial point, acquiring a second oscillation having a second fiducial point, calculating a time interval representing a time from the first fiducial point to the second fiducial point, and determining whether the time interval is a substantial integral multiple of a nominal time interval.
In yet another embodiment, the method provides acquiring a first electrocardiogram (ECG) beat having a first fiducial point, acquiring a first oscillation having a relationship to the first ECG beat, acquiring a second ECG beat having a second fiducial point, acquiring a second oscillation having a relationship to the second ECG beat, calculating a time interval representing a time from the first fiducial point to the second fiducial point, determining whether the time interval is close to an integral multiple of a nominal time interval, and deciding against selecting the second pressure oscillation when the time interval is not close to an integral multiple of a nominal time interval.
In another aspect of the invention, the invention provides a physiological-signal-analysis device for determining blood pressure values of a patient. The device includes a cuff attachable to an extremity of the patient, a pneumatic system connected to the cuff that supplies a fluid to the cuff, a pressure transducer that captures a pressure signal having pressure oscillations, and a control unit connected to the pneumatic system and the pressure transducer. The control unit is operable to acquire a first oscillation having a first fiducial point, acquire a second oscillation having a second fiducial point, calculate a time interval representing a time from the first fiducial point to the second fiducial point, decide against selecting the second oscillation when the time interval is not a substantial integral multiple of an oscillation period, and calculate a blood pressure value based on selected oscillations.
In a further aspect, the invention provides a software program for operating a physiological-signal-analysis device. The software program includes a pneumatic control module for controlling the operation of the pneumatic system, and an analysis module for analyzing input from the pressure transducer and for calculating a blood pressure. The analysis module includes instructions that are implemented for acquiring a first oscillation having a first fiducial point, acquiring a second oscillation having a second fiducial point, calculating a time interval representing a time from the first fiducial point to the second fiducial point, and determining whether the time interval is close to an integral multiple of a nominal time interval.